Bushing cap



1942- E. E. ARNOLD ETAL 2,300,858

BUSHING CAP Filed Jan. 29, 1941 2 Sheets-Sheet l WITNESSES: 2 /Z INVENTORS QMm/i/i 4 MW? 6 Arno/0 &

, 4' Harry J. Z/ngcr/ ATTORNEY 1942- E. E. ARNOLD ETAL 2,300,858

"BUSHING CAP Filed Jan. 29, 1941 2 Sheets-Sheet 2 20 my, 3, g 6 -/6 Z5 WITNESSE 5. INVENTORS @dwr Patented Nov. 3 1942 UNITED STATES PATENT OFFICE BUSHING CAP Edwin E. Arnold, Pittsburgh, and Harry J. Lingal, Forest Hills, Pa., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 29, 1941, Serial No. 376,424

Claims.

The present invention relates to high tension insulating bushings, and it has particular relation to a cap structure for such a bushing. Because of the difference in temperature coeflicients of expansion of parts of such bushings, it has always been a diflicult problem to obtain a proper seal at the cap and to obtain uniform electrical contact between the cap structure and the conducting stud. This problem presents particular difiiculty in the numerous cases where it is required that the cap or terminal member completely close the end of the bushing without the conductor passing therethrough. According to the present invention, a proper uniform electrical contact between the conductor and the cap is obtained despite any relative movement due to expansion by means of a spring device biased between the two members.

It is accordingly an object of the present invention to provide a novel and improved cap structure for high tension electrical insulating bushings.

Another object of the invention is to provide a bushing that shall permit relative movement between the sealed Darts thereof without adversely affecting the seal between such parts or the electrical contact between the cap and the conductor.

A further object of the invention is to provide an. insulating bushing cap in which uniform electrical contact is insured between the conductor and the cap by means of a spring device of high conductivity material biased between the two members.

Other objects and advantages of the invention will appear from the following detailed description taken in accordance with the accompanying drawings in which the same reference characters designate corresponding parts throughout. the drawings:

Figure 1 is a side view partially in section and partly in elevation of a terminal cap in accordance with the invention secured to an insulating bushing; and

Figs. 2 and 3 are similar views of modifications of the invention.

The device comprises, in general, an insulating casing 2, a conductor 4 extending axially therethrough and a terminal cap designated by 6 seated on the end of the bushing with a two piece resilient gasket structure 8 disposed therebetween. A screw-threaded terminal I0 is disposed on the upper end of the cap 6. The dielectric casing member 2, only the upper end of which is shown, is preferably constructed of porcelain having a fiat upper end surface l2, and annular surface creepage flanges of a usual type (not shown).

The conductor 4, which may be either solid or tubular, as illustrated, extends axially through the casing 2 and may be provided within the easing with a condenser structure (not shown) of the type well known in condenser bushings. It will be understood that the position of this conductor is fixed with respect to the lower end of the casing by means of the mounting flange or in some other manner well known in the art.

Referring particularly to Fig. 1, the terminal cap 6 is of a hollow construction and defines a substantially cylindrical interior chamber M at its upper end and a somewhat larger chamber I6 therebelow. The conductor stud is screwthreaded at 18 and a nut 20 disposed thereon, while the end of the cap 6 is closed around the conductor by means of a plate or flange 22 which is secured to the main cap structure by means of bolts 24. A collar member 25 having vertical flanges at 28 is disposed around the conductor 4 below the nut 20 and a helical spring designated by 28 is compressed between it and the plate 22 to supply a uniform sealing pressure to the gasket 8. An insulating washer 29 is preferably disposed between the spring 26 and the plate 22 to prevent electrical contact therebetween. Another resilient gasket member may be disposed between the main cap structure and the plate member 22, as indicated at 30.

To the upper end of the conductor 4 is secured a spring retaining clip 32 while a spring member 34 is disposed in the upper chamber l4 between its surface and the surface of the conductor. The spring 34 is preferably of a good electricalcond-ucting material and its helical turns are in a conical form. This spring is compressed between the upper retaining clip 32 and a similar clip 33 located just above the threaded portion [8 of the conductor 4 so as to be biased against both the surface of the chamber l4 and that of the conductor. This spring may be readily formed by winding the resilient strip material upon a conical shaped helical mandrel and inner and outer-edges thereof are preferably machined to eliminate the corners and provides flat engagement with the surfaces in question. as indicated at 3B and 38, respectively. It will be understood that while retaining clips 32 and 33 are particularly satisfactory with applicants structure, other retaining means may be substituted therefor under some circumstances.

The assembly of the unit is preferably made by securing the spring 34 in place on the end of the stud before placing the cap 6 thereover while the remainder of the structure may be assembled in a manner which will be evident to those skilled in the art.

The construction of Fig. 2 differs from the above in that a pair of helical springs of triangular cross section are employed to provide contact between the cap and stud. The inner of these two springs is designated by 10 and is wound with its flat edge contacting the stud while the outer spring 42 is wound with its flat edge to the outside and engaging the walls of the chamber I l. The two springs are compressed by the upper and lower retaining clips 44 and 46, respectively, and are so disposed that each turn of one of them falls partly within the space between adjacent turns of the other so that a pressure is exerted both inwardly against the stud 4 and outwardly against the cap.

In the modification of Fig. 3, a nut 25, which is used to compress the spring 28 in the same manner as described with reference to the other figures of the drawings is provided with split fingers M3 for engaging the surface of the chamber l4. These fingers may either be themselves resilient with an outward bias, or else, they may be grooved, as indicated at 45, to receive a spring 50. This spring is of the split ring type which facilitates assembly of .the device in a manner which will appear evident from the foregoing description.

With the constructions shown in the present invention, the spring devices insure a definite and uniform electrical contact between a conductor and the terminal cap despite any relative axial movement therebetween which may result from the different coeflicients of expansion of the casing 2 and the conductor itself. The spring contact arrangement further cooperates with the means for clamping the cap in place on the dielectric casing to provide a compact and efficient arrangement. With the insulating washer 29 disposed between the cap and the main sealing spring 25 no current can pass through the latter member With the result that no damaging heating thereof can occur. Even when this washer is not provided the low resistance path provided by the invention prevents the current through this spring 25 from reaching a value high enough to impair its strength,

Since various modifications of the structure shown in the drawings will appear to those skilled in the art, it is intended that the invention be limited only by the appended claims, interpreted in view of the prior art.

We claim as our invention:

1. In a bushing for high tension electrical apparatus including a tubular casing of insulating material and a rigid conducting stud extending axially through said casing in fixed relationship thereto, a metallic terminal cap engaging an end of said casing to close it, said cap defining a substantially cylindrical interior chamber about the end of said stud, and metallic helical spring means disposed around said stud in resilient engagement with its surface and the surrounding surface of said chamber and in slidable relation to at least one of said surfaces, whereby said spring means maintains a slidable resilient electrical contact with one of said surfaces in response to relative axial movement between said stud and cap due to the difference in temperature expansion characteristics of the stud and easing.

2. In a bushing for high tension electrical apparatus including a tubular casing of insulating material and a rigid conducting stud extending axially through said casing in fixed relationship thereto, a metallic cap engaging an end of said casing to close it, said cap defining a substan tially cylindrical chamber about the end of said stud, and a helical spring comprising substantially conically disposed turns of resilient metal strip arranged around said stud with its opposite edges biased against the surface of said stud and the surface of said chamber respectively to insure uniform electrical contact therebetween despite relative movement between the cap and stud.

3. In a bushing for high tension electrical apparatus including a tubular casing of insulating material and a conducting stud extending axially through said casing in fixed relationship thereto, a metallic cap engaging an end of said casing to close it, said cap defining a substantially cylindrical chamber about the end of said stud, and a pair of helical springs of substantially triangular cross section disposed within said chamber about said stud, one of said springs being arranged with one of its sides contacting said stud and the other being arranged with one of its sides contacting the surface of said chamber in staggered relationship to the first said spring so that the turns of each spring are partially disposed within the substantially triangular spaces between turns of the other.

4. In a bushing for high tension electrical apparatus including a tubular casing of insulating material and a rigid conducting stud extending axially through said casing in fixed relationship thereto, a metallic terminal cap engaging an end of said casing to close it and defining a chamber with an even cylindrical surface about the end of said stud, helical spring means disposed around said stud in resilient engagement with its surface and the surroundin surface of said chamber, and means projecting from said stud in engagement with the ends of said spring means to confine it to a predetermined longitudinal portion thereof, whereby said spring means moves with said stud in sliding electrical contact with said chamber surface in response to relative axial movement between said stud and cap due to the difference in temperatur expansion characteristics of the stud and casing.

5. In a bushing for high tension electrical apparatus including a tubular casing of insulating material and a conducting stud extending axially through said casing in fixed relationship thereto, a metallic cap engaging an end of said casing to close it, said cap defining a substantially cylindrical chamber about the end of said stud, a first helical spring disposed in said chamber about said stud and having sloping surface portions defining an outwardly divergent helical space between adjacent turns, and a second helical spring disposed in said chamber in engagement with the surface thereof and having a cross section such that a sloping portion thereof extends into said helical space in resilient engagement with the turns of said other spring defining it.

EDWIN E. ARNOLD. HARRY J. LINGAL. 

